1. Field of the Invention
The present invention relates to a manufacturing method of an optical element called a microlouver whose transmission light emitting direction range is limited, an exposure device used for manufacturing the optical element, an optical element, a liquid crystal display device (LCD: Liquid Crystal Display) using the optical element, a display device such as a plasma display, a lighting optical device, and an electronic apparatus.
2. Description of the Related Art
Conventionally, liquid crystal display devices are used as display devices of various kinds of information processing devices such as mobile phones, portable information terminals (PDAs: Personal Digital Assistants), ATMs (Automatic Teller Machines), and personal computers. Recently, liquid crystal display devices of a wide visible range have been put into practical use.
For this type of liquid crystal display device, various light distribution properties have come to be required due to increased scale and multiple purposes of recent displays. In particular, there have been increased demands for limiting the visible range so as not to be peeped from others and demands for not emitting light to unnecessary directions in regards to information leakages. For meeting those demands, displays to which a microlouver is added to restrict the visible range (or emission range) have been proposed, and a part of which has been put into practical use.
In a case where a microlouver is applied to a large-scaled display, a center part of the large-scaled display is displayed brightly so that it is possible to recognize an image when an observer observes the large-scaled display from a position corresponding to almost the center part of the large-scaled display.
In the meantime, the peripheral part of the large-scaled display is displayed dark in general, so that it is difficult to recognize an image. As a result, there may be cases where the observer cannot finely recognize the entire image displayed on the large-scaled display.
As shown in the sectional structure of FIG. 20, this is because a light absorption layer 201a of a microlouver 201 provided on the front face of a display 200 is formed almost in a perpendicular direction with respect to the surface of the display 200.
In the case of FIG. 20, the viewing angle with a microlouver in which the height of the light absorption layer is 120 μm, for example, the width is 10 μm, and the pitch is 50 μm is ±18 degrees. However, when the microlouver is added to the front face of the display and viewed at a distance of 60 cm from the screen, it is known that the angle of view at both ends of the display becomes ±24 degrees or more with the display size of 26 inches diagonally (aspect ratio of 3:4). Therefore, the image cannot be visually recognized.
In order to avoid such phenomenon, the light absorption layer needs to be tilted towards the center of the screen so as not to interrupt visual recognition of the observer even when the observer views the both ends of the display. When viewing the display of the above-described size of 26 inches diagonally (aspect ratio of 3:4) at a distance of 60 cm from the screen, a tilt angle of 24 degrees is required for visually recognizing the both ends of the display in the brightness equivalent to that of the center of the display.
Japanese Unexamined Patent Publication 2008-116913 (Patent Document 1: Method for Manufacturing Optical Element) discloses a manufacturing method of a microlouver having the prescribed light distribution property. In the case of the microlouver disclosed in Patent Document 1, first, a mask is disposed on a transparent photosensitive resin, and exposure light is irradiated over the mask to pattern the transparent photosensitive resin so as to form a transparent layer.
Further, diffused light from a point light source or light refracted by a Fresnel lens is used for the exposure light at this time, so that the light makes incident obliquely on the mask face. Thereafter, a black curable resin is filled between the transparent layers to form the light absorption layers. Through those steps, a microlouver having the light distribution property with which light is converged to a prescribed position can be obtained.
Further, Japanese Unexamined Patent Publication 2007-334279 (Patent Document 2: Method for Manufacturing Light-Ray Direction Control Element) discloses a structure of a microlouver in which laminate patterns of an aluminum light-shielding pattern and a light absorption pattern are formed on a substrate, and a transparent layer is formed between the laminate patterns. As disclosed in Japanese Unexamined Patent Publication 2005-343115 (Patent Document 3: Method for Creating Resist Pattern) and Japanese Unexamined Patent Publication Hei 02-247647 (Patent Document 4: Method for Manufacturing Mask), the microlouver depicted in Patent Document 2 can be formed by: forming a transparent photosensitive resin on a transparent substrate after forming a light-shielding pattern on the surface of the transparent substrate; exposing it by irradiating light from the back side of the transparent substrate; and developing the transparent photosensitive resin thereafter to form the transparent layer on the transparent substrate.
However, in a case where the transparent layer is formed by patterning the transparent photosensitive resin by using the exposure light that makes incident on the mask face in the oblique direction from a point light source, obtained is the pattern tilted entirely except for the center of the substrate with the technique of the method for manufacturing the optical element disclosed in Patent Document 1. Therefore, it is difficult to form patterns on other various kinds of shapes, such as a pattern having a transparent layer that is not tilted except for the center of the substrate, for example.
Such difficulty also occurs in the case where the transparent photosensitive resin is exposed by utilizing a light-shielding pattern formed in advance on the transparent layer as in the cases of Patent Document 2 and Patent Document 4.
Further, with the above-described technique disclosed in Patent Document 1, it is impossible to completely make the light-shielding pattern on the mask and the transparent photosensitive resin fitted closely due to deterioration in the surface flatness caused by edge bead generated in an edge part of the region to which the transparent photosensitive resin is applied and variation in the film thickness within the applied region and due to undulation of the substrate surface on which the transparent photosensitive resin is formed. Deterioration in the resolution and variation in the patterns are generated because of the gap generated as a result, thereby causing a decrease in the yield and inducing a cost increase.
Furthermore, with the technique depicted in Patent Document 1 described above, the transparent layer is formed by refracting the incident light to the oblique direction by the Fresnel lens, and it is used as the exposure light to form the transparent layer. However, formation of the refracted light depends on the complicated shape of the Fresnel lens, so that deterioration in the yield tends to occur depending on the fault in the shape of the Fresnel lens. This deteriorates the productivity and induces a cost increase at the same time.
An exemplary object of the present invention is to improve the above-described inconveniences, and to provide a manufacturing method of an optical element capable of easily forming various kinds of shapes in accordance width the demands, and capable of increasing the functions without using a complicated component such as a Fresnel lens as well as improving the yield and reducing the cost, and to provide an optical element exposure device to which the manufacturing method is employed, an optical element manufactured by the exposure device, and a lighting optical device, a display device, and an electronic apparatus to which the optical element is loaded.